July 21, 2009

Study Says That Fish Are Shrinking

A study published Monday reported that fish have lost half their average body mass and smaller species are making up a larger proportion of European fish stocks as a result of global warming.

Martin Daufresne of the Cemagref Public Agricultural and Environmental Research Institute in Lyon, France said, "Size is a fundamental characteristic that is linked to a number of biological functions, such as fecundity - the capacity to reproduce."

Smaller fish tend to produce fewer eggs, and they also provide less sustenance for predators, including humans.

A similar effect has recently been documented in Scottish Sheep and Daufresne said that it is possible that global warming might have a "significant impact on organisms in general."

Earlier research showed that fish have shifted their geographic ranges and their migratory and breeding patterns in response to rising water temperatures. Also, it has been established that warmer regions tend to be inhabited by smaller fish.

Daufresne, along with his colleagues, examined long-term surveys of fish populations in rivers, streams and the Baltic and North Seas while performing experiments on bacteria and plankton.

In their study, they found the individual species lost an average of 50 percent of their body mass over the past 20 to 30 years, while the average size of the overall fishing stock had shrunk by 60 percent.

Daufrense said that this was a result of a decrease in the average size-at-age and an increase in the proportion of juveniles and small-sized species.

"It was an effect that we observed in a number of organisms and in a number of very different environments - on fish, on plankton, on bacteria, in fresh water, in salt water - and we observed a global shrinking of size for all the organisms in all the environments," Daufresne said in a telephone interview.

The study, which was published in the Proceedings of the National Academy of Sciences, found that while commercial and recreational fishing impacts some of the fisheries that were studied, it "cannot be considered as the unique trigger" for the changes in size.

"Although not negating the role of other factors, our study provides strong evidence that temperature actually plays a major role in driving changes in the size structure of populations and communities," the study concluded.